The response of microorganisms to specific growth challengesand enviromental stresses is relatvely unknown. Although such practices form the basis of our concept regarding sterilization and food preservation, only a vague picture of the molecular consequences of such treatment is at hand. These data mostly pertain to heat treatment which results in ribosomal and other alterations in the cell. I propose to study the ribosomal aspects further. The basic technique involves the use of sub-lethal levels of heat to injure upwards of 90% of the bacterial population. The injury is reflected by degradation and alteration of the ribosomal subunits and is reversible under the proper conditions. The research objectives of this proposal are two-fold and relate both to the injury process and the recovery phase of the thermal injury profile. They are 1) a determination of the configurational modifications and functional fidelity of 50S subunits from heat injured cells and 2) investigation of the mechanism of assembly, conformation, and functional fidelity of the reassembled 30S particles. The techniques used in the performance of this work involve polyacrylamide disc gel electrophoresis, ion-exchange chromatography on phosphocellulose columns and enzymic assays of function involving radioisotopic techniques. Ribosomal subunits will be isolated and purified by conventional ultracentrifugal techniques employing sucrose densitygradients for subunit separation.